--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/SystemChangeNotifier.st	Mon Oct 12 21:11:38 2009 +0200
@@ -0,0 +1,70 @@
+"{ Package: 'stx:libbasic' }"
+
+Object subclass:#SystemChangeNotifier
+	instanceVariableNames:'silenceLevel'
+	classVariableNames:'UniqueInstance'
+	poolDictionaries:''
+	category:'Kernel-Classes'
+!
+
+!SystemChangeNotifier class methodsFor:'documentation'!
+
+documentation
+"
+    For now, this implementation is mostly for squeak compatibility.
+    However, over time, we will move the change notification code from ClassDescription to here,
+    to make things easier to understand, and classDescription a little bit more lightweight.
+"
+! !
+
+!SystemChangeNotifier class methodsFor:'instance creaton'!
+
+uniqueInstance
+    "I am a singleton"
+
+    UniqueInstance isNil ifTrue: [UniqueInstance := self basicNew initialize].
+    ^ UniqueInstance
+
+    "
+     UniqueInstance releaseAll.
+     UniqueInstance := nil
+    "
+! !
+
+!SystemChangeNotifier methodsFor:'initialization'!
+
+initialize
+    "/ eventSource := SystemEventManager new.
+    silenceLevel := 0.
+! !
+
+!SystemChangeNotifier methodsFor:'public'!
+
+doSilently: aBlock
+    "Perform the block, and ensure that no system notification are broadcasted while doing so."
+
+    |result|
+
+    silenceLevel := silenceLevel + 1.
+    [
+        "/ temporary hack:
+        Class withoutUpdatingChangesDo:[
+            result := aBlock value
+        ]
+    ] ensure: [
+        silenceLevel > 0 ifTrue: [
+            silenceLevel := silenceLevel - 1
+        ]
+    ].
+    ^ result.
+!
+
+isBroadcasting
+    ^ silenceLevel = 0
+! !
+
+!SystemChangeNotifier class methodsFor:'documentation'!
+
+version_CVS
+    ^ '$Header: /cvs/stx/stx/libbasic/SystemChangeNotifier.st,v 1.1 2009-10-12 19:11:38 cg Exp $'
+! !